Field of the Invention
Embodiments of the invention generally relate to implantable medical devices, and, more particularly, implantable medical devices utilizing leads.
Description of the Related Art
Generally, implantable medical devices (IMD) for delivering a therapy or monitoring a physiologic condition of a human or animal body employ one or more elongated electrical leads in contact with the body tissue. Such IMD, typically, may monitor or deliver therapy to the heart, muscle, nerve, brain, and stomach or other organs. IMD such as pacemakers and implantable cardioverter defibrillators (ICD), for example, are typically used to treat cardiac arrhythmias by delivering electrical impulses to the heart. Such devices generally include sensing units that sense electrical cardiac activities through cardiac leads having one or more electrodes. When an abnormal rhythm is detected, typically, an appropriate electrical therapy is delivered by a therapy unit connected to cardiac leads.
Leads associated with such IMD typically include a lead body extending between a proximal lead end and a distal lead end. The lead body generally incorporates one or more exposed electrode or sensor elements located at or near the distal lead end. One or more elongated electrical conductors may typically extend through the lead body from a connector assembly provided at a proximal lead end for connection with an associated IMD and an electrode located at the distal lead end or along a section of the lead body. Each electrical conductor is typically electrically isolated from any other electrical conductors and is encased within an outer sheath that electrically insulates the lead conductors from body tissue and fluids.
Implantable medical leads typically extend from an implantation site of the IMD through an internal body pathway to a desired tissue site. The leads are generally small in diameter, highly flexible, and reliable lead bodies that withstand degradation by body fluids and body movements that apply stress and strain to the lead body and the connections made to electrodes. As lead bodies are made smaller and smaller and/or the number of lead conductors is increased, the integrity of lead conductors is generally increasingly important.
Implantable medical leads that extend to or in the heart (cardiac leads) are typically continuously flexed by the beating of the heart. Other stresses are generally applied to the lead body during an implantation or lead repositioning procedure, and by movements of the patient. For that reasons the lead may typically be slightly damaged, and the slight damage may progress until a lead conductor fractures and/or the insulation is breached causing an interruption of the electric conduction path or a short between conductors that are normally isolated. Also the connection of the lead to the IMD at the connector assembly may generally be interrupted or shortened. These effects may typically progress from an intermittent manifestation to a more continuous effect and may be referred to as “lead failures”.
Lead failures typically adversely impact the normal operation of the IMD. Any interruption or short generally impedes sensing of electrical signals from the tissue and the stimulation of the tissue with electrical pulses. In the case of cardiac leads, generally, an interruption or a short may be misinterpreted by the IMD as intrinsic activity of the heart. This is generally known as oversensing or undersensing and may result in an incorrect interpretation of the cardiac data potentially resulting in inappropriate withholding or delivery of electrical therapy.
Generally, several methods have been developed to monitor lead integrity and detect lead failures. The most common method is the monitoring of lead impedance as significant changes of lead impedance are typically an indicator of lead failures. Impedance monitoring generally consumes energy and may interfere the sensing and is therefore not suited for continuous monitoring. In the case of discontinuous impedance monitoring, typically, intermittent lead failures may remain undetected.
Another method typically analyzes the intra cardiac electrogram (IEGM) waveform by comparing them with reference waveforms that represent physiological signals. This method generally requires the generation of reference waveforms. Due to the large variance of physiological waveforms, this method is typically susceptible for miss-detections.
In view of the above, there is a need for an improved method and device that detects lead failures.